CN113892202A - Binder composition for heat-resistant layer of nonaqueous secondary battery, slurry composition for heat-resistant layer of nonaqueous secondary battery, heat-resistant layer for nonaqueous secondary battery, and nonaqueous secondary battery - Google Patents

Binder composition for heat-resistant layer of nonaqueous secondary battery, slurry composition for heat-resistant layer of nonaqueous secondary battery, heat-resistant layer for nonaqueous secondary battery, and nonaqueous secondary battery Download PDF

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CN113892202A
CN113892202A CN202080038948.XA CN202080038948A CN113892202A CN 113892202 A CN113892202 A CN 113892202A CN 202080038948 A CN202080038948 A CN 202080038948A CN 113892202 A CN113892202 A CN 113892202A
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heat
resistant layer
secondary battery
particulate polymer
nonaqueous secondary
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CN113892202B (en
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北泽侑造
浅井一辉
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Zeon Corp
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Zeon Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
    • H01M50/461—Separators, membranes or diaphragms characterised by their combination with electrodes with adhesive layers between electrodes and separators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/30—Sulfur-, selenium- or tellurium-containing compounds
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
    • C08L33/18—Homopolymers or copolymers of nitriles
    • C08L33/20—Homopolymers or copolymers of acrylonitrile
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/18—Oxygen-containing compounds, e.g. metal carbonyls
    • C08K3/20—Oxides; Hydroxides
    • C08K3/22—Oxides; Hydroxides of metals
    • C08K2003/2227—Oxides; Hydroxides of metals of aluminium
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/30—Sulfur-, selenium- or tellurium-containing compounds
    • C08K2003/3045—Sulfates
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical Kinetics & Catalysis (AREA)
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  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
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  • Health & Medical Sciences (AREA)
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  • Battery Electrode And Active Subsutance (AREA)
  • Cell Separators (AREA)

Abstract

The present invention provides an adhesive composition for a heat-resistant layer of a nonaqueous secondary battery, comprising a particulate polymer, wherein the particulate polymer comprises a cyano group-containing monomer unit and a hydroxyl group-containing monomer unit, and further comprises a value M of the molar fraction of the hydroxyl group-containing monomer unit in the particulate polymerOHValue S (μm) divided by the surface area of the particulate polymer2) To the obtained value (M)OH(S) is 0.40 or more.

Description

Binder composition for heat-resistant layer of nonaqueous secondary battery, slurry composition for heat-resistant layer of nonaqueous secondary battery, heat-resistant layer for nonaqueous secondary battery, and nonaqueous secondary battery
Technical Field
The present invention relates to a binder composition for a heat-resistant layer of a nonaqueous secondary battery, a slurry composition for a heat-resistant layer of a nonaqueous secondary battery, a heat-resistant layer for a nonaqueous secondary battery, and a nonaqueous secondary battery.
Background
Nonaqueous secondary batteries such as lithium ion secondary batteries (hereinafter, may be simply referred to as "secondary batteries") are small in size, light in weight, high in energy density, and capable of being repeatedly charged and discharged, and are used in a wide range of applications. In addition, the secondary battery generally includes battery members such as electrodes (a positive electrode and a negative electrode) and a separator for separating the positive electrode and the negative electrode. As such a battery member, a battery member having a heat-resistant layer, which is a protective layer for improving heat resistance, has been used.
Here, as the heat-resistant layer of the secondary battery, there is a heat-resistant layer in which nonconductive particles are bonded with a binder. Such a heat-resistant layer is generally formed by: a slurry composition in which non-conductive particles and a binder are dissolved or dispersed in a dispersion medium such as water (hereinafter, sometimes referred to as "slurry composition for a heat-resistant layer of a non-aqueous secondary battery", and sometimes simply referred to as "slurry composition for a heat-resistant layer") is prepared, and the slurry composition for a heat-resistant layer is applied to a substrate such as a separator substrate or an electrode substrate and dried.
In recent years, in order to further improve the performance of secondary batteries, an attempt has been made to improve a binder composition for forming a heat-resistant layer (see, for example, patent document 1).
Patent document 1 discloses a slurry for a porous membrane of a lithium ion secondary battery, which contains nonconductive particles, a water-soluble polymer having an acid group-containing monomer unit, and a particulate polymer, wherein the amount of the water-soluble polymer is within a predetermined range relative to the amount of the nonconductive particles, and the BET specific surface area of the nonconductive particles is within a predetermined range. More specifically, patent document 1 discloses a slurry for porous membranes, which contains a particulate polymer obtained by polymerization under predetermined conditions using a monomer composition containing acrylonitrile as a nitrile group-containing monomer, butyl acrylate as a (meth) acrylate monomer, methacrylic acid as an ethylenically unsaturated acid monomer, and allyl glycidyl ether and N-methylolacrylamide as crosslinkable monomers, a water-soluble polymer, and nonconductive particles. The slurry for a porous film described in patent document 1 can form a heat-resistant layer, which is a porous film that can exhibit heat resistance. Further, according to the slurry for a porous membrane described in patent document 1, the obtained lithium ion secondary battery can be made excellent in high-temperature cycle characteristics.
Documents of the prior art
Patent document
Patent document 1: international publication No. 2014/148577.
Disclosure of Invention
Problems to be solved by the invention
However, in recent years, further improvement in the performance of secondary batteries has been demanded, and there is still room for improvement in the adhesion between the heat-resistant layer formed using the paste composition and the base material (for example, a separator base material or an electrode base material) on which the heat-resistant layer is formed, with respect to the above-mentioned conventional paste composition. More specifically, the slurry composition is required to have an improved peel strength of the obtained heat-resistant layer and an improved adhesion between the heat-resistant layer and the substrate.
Accordingly, an object of the present invention is to provide a binder composition for a heat-resistant layer of a nonaqueous secondary battery, which can prepare a slurry composition for a heat-resistant layer of a nonaqueous secondary battery capable of forming a heat-resistant layer for a nonaqueous secondary battery having sufficiently high peel strength.
It is another object of the present invention to provide a slurry composition for a heat-resistant layer of a nonaqueous secondary battery, which can form a heat-resistant layer for a nonaqueous secondary battery having sufficiently high peel strength.
It is another object of the present invention to provide a heat-resistant layer for a nonaqueous secondary battery having sufficiently high peel strength, and a nonaqueous secondary battery having the heat-resistant layer.
Means for solving the problems
The present inventors have conducted intensive studies with a view to solving the above problems. The present inventors have found that a heat-resistant layer having sufficiently high peel strength can be formed when a particulate polymer containing a hydroxyl group-containing monomer unit and a cyano group-containing monomer unit and having a value (parameter) obtained by dividing the molar fraction of the hydroxyl group-containing monomer unit in the particulate polymer by the surface area of the particulate polymer satisfies a predetermined condition.
That is, the present invention is directed to solving the above problems advantageously, and an adhesive composition for a heat-resistant layer of a nonaqueous secondary battery according to the present invention includes a particulate polymer, wherein the particulate polymer includes a cyano group-containing monomer unit and a hydroxyl group-containing monomer unit, and further a value M of a mole fraction of the hydroxyl group-containing monomer unit in the particulate polymerOHDivided by the value S (. mu.m) of the surface area of the above particulate polymer2) To the obtained value (M)OH(S) is 0.40 or more. As described above, according to the adhesive composition comprising the particulate polymer comprising the hydroxyl group-containing monomer unit and the cyano group-containing monomer unit and the value (M) calculated as specified aboveOHHas an S) of 0.40 or more, and can form a heat-resistant layer having a sufficiently high peel strength.
In addition, the polymer "containing a monomer unit" means "containing a structural unit derived from a monomer in a polymer obtained using the monomer".
The "mole fraction" of a certain monomer unit (each repeating unit) contained in a polymer is a ratio of the number of moles of the certain monomer unit contained in the polymer when the total number of moles of all repeating units (all monomer units) contained in the polymer is 1.
Further, "mole fraction" can be used1H-NMR、13Nuclear Magnetic Resonance (NMR) method such as C-NMR.
Here, in the binder composition for a heat-resistant layer of a nonaqueous secondary battery of the present invention, it is preferable that the volume average particle diameter of the particulate polymer is 0.30 μm or less and the molar fraction of the hydroxyl group-containing monomer unit in the particulate polymer is 0.02 or more. When the volume average particle diameter of the particulate polymer is 0.30 μm or less and the mole fraction of the hydroxyl group-containing monomer unit in the particulate polymer is 0.02 or more, the heat shrinkage resistance of the heat-resistant layer to be obtained can be improved, and the cycle characteristics of the secondary battery to be obtained can be improved.
The "volume average particle diameter" of the particulate polymer means "a particle diameter (D50) in which the cumulative volume calculated from the small particle diameter side becomes 50% in the particle size distribution (volume basis) measured by a laser diffraction method".
In the binder composition for a heat-resistant layer of a nonaqueous secondary battery according to the present invention, the molar fraction of the cyano group-containing monomer unit in the particulate polymer is preferably 0.07 or less. If the mole fraction of the cyano group-containing monomer unit in the particulate polymer is 0.07 or less, the heat shrinkage resistance of the obtained heat-resistant layer can be further improved.
Further, the binder composition for a heat-resistant layer of a nonaqueous secondary battery of the present invention preferably has a swelling degree of the particulate polymer in an electrolyte solution of 8.0 times or less. If the swelling degree of the particulate polymer in the electrolyte is 8.0 times or less, the cycle characteristics of the obtained secondary battery can be improved.
The swelling degree was determined by dissolving LiPF in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a concentration of 1mol/L in an electrolyte solution (the weight ratio of ethylene carbonate to ethyl methyl carbonate was 3: 7)6The obtained solution) can be measured by the method described in examples.
The present invention is also directed to solving the above problems, and a slurry composition for a heat-resistant layer of a nonaqueous secondary battery according to the present invention is characterized by containing a binder composition for a heat-resistant layer of a nonaqueous secondary battery, which contains nonconductive particles. In this manner, according to the slurry composition containing the non-conductive particles and any one of the above binder compositions, a heat-resistant layer having sufficiently high peel strength can be formed.
In the slurry composition for a heat-resistant layer of a nonaqueous secondary battery according to the present invention, the volume average particle diameter of the non-conductive particles is preferably 0.7 μm or less. If the volume average particle diameter of the non-conductive particles is 0.7 μm or less, the heat shrinkage resistance of the obtained heat-resistant layer can be improved.
The volume average particle diameter of the nonconductive particles means "a particle diameter (D50) in which the cumulative volume calculated from the small particle diameter side becomes 50% in the particle size distribution (volume basis) measured by a laser diffraction method".
The present invention is also directed to solving the above-mentioned problems, and a heat-resistant layer for a nonaqueous secondary battery according to the present invention is formed using the slurry composition for a heat-resistant layer for a nonaqueous secondary battery. In this manner, the peel strength of the heat-resistant layer formed from the slurry composition is sufficiently high.
In addition, an object of the present invention is to advantageously solve the above-described problems, and a nonaqueous secondary battery of the present invention is characterized by having the above-described heat-resistant layer for a nonaqueous secondary battery. In this way, the secondary battery having the battery member including the heat-resistant layer is excellent in battery characteristics.
Effects of the invention
According to the present invention, it is possible to provide a binder composition for a heat-resistant layer of a nonaqueous secondary battery, which can prepare a slurry composition for a heat-resistant layer of a nonaqueous secondary battery capable of forming a heat-resistant layer for a nonaqueous secondary battery having sufficiently high peel strength.
Further, according to the present invention, it is possible to provide a slurry composition for a heat-resistant layer of a nonaqueous secondary battery, which can form a heat-resistant layer for a nonaqueous secondary battery having sufficiently high peel strength.
Further, according to the present invention, it is possible to provide a heat-resistant layer for a nonaqueous secondary battery having sufficiently high peel strength, and a nonaqueous secondary battery having the heat-resistant layer.
Detailed Description
The embodiments of the present invention will be described in detail below.
Here, the binder composition for a heat-resistant layer of a nonaqueous secondary battery of the present invention can be used for the preparation of the slurry composition for a heat-resistant layer of a nonaqueous secondary battery of the present invention. The slurry composition for a heat-resistant layer of a nonaqueous secondary battery of the present invention can be used for forming a heat-resistant layer of a nonaqueous secondary battery such as a lithium ion secondary battery. The slurry composition for a heat-resistant layer of a nonaqueous secondary battery of the present invention is a slurry composition for a heat-resistant layer of a nonaqueous secondary battery. The nonaqueous secondary battery of the present invention is characterized by having a heat-resistant layer for a nonaqueous secondary battery produced using the slurry composition for a heat-resistant layer of a nonaqueous secondary battery of the present invention.
(Binder composition for nonaqueous Secondary Battery Heat-resistant layer)
The binder composition of the present invention comprises a particulate polymer and may optionally also comprise a dispersing medium and other ingredients.
The binder composition of the present invention is characterized in that the particulate polymer contains a hydroxyl group-containing monomer unit and a cyano group-containing monomer unit, and the value M of the molar fraction of the hydroxyl group-containing monomer unit in the particulate polymer isOHValue S (μm) divided by the surface area of the particulate polymer2) To the obtained value (M)OH(S) is 0.40 or more.
Further, since the binder composition of the present invention contains the particulate polymer satisfying the above-described predetermined properties, the obtained heat-resistant layer can be bonded to the substrate with sufficient strength, and as a result, the peel strength of the heat-resistant layer can be sufficiently improved. The above-mentioned effects can be obtained by using the binder composition containing the particulate polymer as described above, and the reason for this is not clear, but it is presumed that the value M is the molar fraction of the hydroxyl group-containing monomer unitOHValue S (μm) divided by the surface area of the particulate polymer2) To the obtained value (M)OHThe particulate polymer containing a hydroxyl group-containing monomer unit to the extent of 0.40 or more/S) can strongly adhere to an adherend.
< particulate Polymer >
The particulate polymer contained in the binder composition of the present invention is a component that functions as a binder in a heat-resistant layer formed using a slurry composition, and is a component that imparts adhesiveness to the heat-resistant layer formed using a slurry composition containing a binder composition and keeps non-conductive particles contained in the heat-resistant layer from coming off the heat-resistant layer.
The particulate polymer is a water-insoluble particle formed of a predetermined polymer. In the present invention, the term "water-insoluble" means that the insoluble matter is 90% by mass or more when 0.5g of the polymer is dissolved in 100g of water at a temperature of 25 ℃.
Here, the particulate polymer contains a cyano group-containing monomer unit and a hydroxyl group-containing monomer unit, and may optionally contain other monomer units. The various monomer units are described in detail below.
Monomer unit containing cyano group
The cyano group-containing monomer unit is a monomer unit obtained by polymerizing a cyano group-containing monomer. Examples of the cyano group-containing monomer that can form a cyano group-containing monomer unit include α, β -unsaturated nitrile monomers such as acrylonitrile and methacrylonitrile. These may be used alone or in combination of two or more in an arbitrary ratio.
The molar fraction of the cyano group-containing monomer unit in the particulate polymer is preferably 0.07 or less, more preferably 0.06 or less, and still more preferably 0.05 or less, with the total molar number of all the repeating units contained in the particulate polymer being 1. If the molar fraction of the cyano group-containing monomer unit in the particulate polymer is not more than the upper limit, the heat shrinkage resistance of the obtained heat-resistant layer can be improved. The molar fraction of the cyano group-containing monomer unit is desirably more than 0, preferably 0.01 or more. The presence of the cyano group-containing monomer unit in the production of the particulate polymer can improve the stability of the particulate polymer during polymerization.
[ hydroxyl group-containing monomer Unit ]
The hydroxyl group-containing monomer unit is a monomer unit obtained by polymerizing a hydroxyl group-containing monomer. Examples of the hydroxyl group-containing monomer that can form a hydroxyl group-containing monomer unit include: hydroxyalkyl acrylates such as hydroxymethyl acrylate, hydroxymethyl methacrylate, β -hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate and hydroxybutyl methacrylate; and N-hydroxyalkyl acrylamides such as N-hydroxymethyl acrylamide (N-hydroxymethyl acrylamide), N-hydroxymethyl methacrylamide (N-hydroxymethyl methacrylamide), N-hydroxyethyl acrylamide, and N-hydroxyethyl methacrylamide. These may be used alone or in combination of two or more in an arbitrary ratio. Also, among these, N-methylolacrylamide, beta-hydroxyethyl acrylate, hydroxyethyl methacrylate and N-hydroxyethyl acrylamide are preferable, and N-methylolacrylamide and beta-hydroxyethyl acrylate are more preferable.
The molar fraction of the hydroxyl group-containing monomer unit in the particulate polymer is preferably 0.02 or more, more preferably 0.03 or more, preferably 0.10 or less, and more preferably 0.08 or less, with the total molar number of all the repeating units contained in the particulate polymer being 1. When the molar fraction of the hydroxyl group-containing monomer unit in the particulate polymer is not less than the lower limit, the adhesion between the obtained heat-resistant layer and the base material is improved, and the cycle characteristics of the obtained secondary battery can be improved. Further, if the molar fraction of the hydroxyl group-containing monomer units in the particulate polymer is not more than the above upper limit, the polymerization stability in producing the particulate polymer can be improved.
Other monomer units
The other monomer unit is not particularly limited, and examples thereof include a (meth) acrylate monomer unit, an acidic group-containing monomer unit, an ethylenically unsaturated carboxylic acid amide monomer unit, a crosslinkable monomer unit, an aromatic vinyl monomer unit, a fluorine atom-containing monomer unit, and an aliphatic conjugated diene monomer unit. In addition, in the present specification, (meth) acrylic acid means acrylic acid or methacrylic acid.
[ (meth) acrylate monomer units ]
The (meth) acrylate monomer unit is a monomer unit obtained by polymerizing a (meth) acrylate monomer. Examples of the (meth) acrylate monomer capable of forming a (meth) acrylate monomer unit include acrylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate (n-butyl acrylate), isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate (2-ethylhexyl acrylate), 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, hexyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate, and benzyl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate and benzyl methacrylate. These may be used alone or in combination of two or more in an arbitrary ratio. Among them, as the (meth) acrylate monomer, n-butyl acrylate (n-butyl acrylate) and 2-ethylhexyl acrylate (2-ethylhexyl acrylate) are preferable.
When the particulate polymer contains a (meth) acrylate monomer unit, the molar fraction of the (meth) acrylate monomer unit in the particulate polymer is preferably more than 0.5, more preferably 0.6 or more, preferably less than 0.98, more preferably 0.95 or less, and further preferably 0.93 or less, with the total molar number of all the repeating units contained in the particulate polymer being 1. If the molar fraction of the (meth) acrylate monomer unit in the particulate polymer is within the above range, the peel strength of the obtained heat-resistant layer can be further improved. In the present specification, a particulate polymer having a mole fraction of (meth) acrylate monomer units of more than 0.5 is referred to as a (meth) acrylate copolymer.
[ acid group-containing monomer Unit ]
The acid group-containing monomer unit is a monomer unit obtained by polymerizing an acid group-containing monomer. Examples of the acidic group include: -COOH groups (carboxylic acid groups); -SO3H group (sulfonic acid group); -PO3H2Phosphoric acid groups such as a group and a-PO (OH) (OR) group (R represents a hydrocarbon group)An acidic functional group. Therefore, examples of the acidic group-containing monomer that can form the acidic group-containing monomer unit include monomers having these acidic groups. Further, examples of the acidic group-containing monomer include monomers which can generate an acidic group as described above by hydrolysis. Specific examples of such an acidic group-containing monomer include acid anhydrides which can generate a carboxylic acid group by hydrolysis. The acid group-containing monomers listed below may be used singly or in combination of two or more kinds at an arbitrary ratio.
Examples of the monomer having a carboxylic acid group include: monocarboxylic acids, dicarboxylic acids, anhydrides of dicarboxylic acids, and derivatives thereof. Examples of monocarboxylic acids include: acrylic acid, methacrylic acid, crotonic acid, 2-ethacrylic acid, isocrotonic acid, and the like. Examples of the dicarboxylic acid include: carboxylic acid group-containing monomers such as maleic acid, fumaric acid, itaconic acid, and methyl maleic acid. Examples of the acid anhydride of the dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.
Examples of the monomer having a sulfonic acid group include: sulfonic acid group-containing monomers such as vinylsulfonic acid, methylvinylsulfonic acid, (meth) allylsulfonic acid, styrenesulfonic acid, ethyl (meth) acrylate-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and 2- (N-acryloyl) amino-2-methyl-1, 3-propane-disulfonic acid.
As having-PO3H2Examples of the monomer having a phosphate group such as a group-PO (OH) (OR) and a group (R represents a hydrocarbon group) include: phosphoric acid group-containing monomers such as 2- (meth) acryloyloxyethyl phosphate, methyl-2- (meth) acryloyloxyethyl phosphate, and ethyl- (meth) acryloyloxyethyl phosphate. In addition, (meth) acryloyl in the present specification means acryloyl or methacryloyl.
In addition, salts of the above-mentioned various monomers can also be used as the acid group-containing monomer. Among the above acidic group-containing monomers, carboxylic acid group-containing monomers are preferably used, monocarboxylic acids such as those described above are more preferably used, and methacrylic acid is particularly preferably used.
When the particulate polymer contains an acidic group-containing monomer unit, the molar fraction of the acidic group-containing monomer unit in the particulate polymer is preferably 0.01 or more and 0.1 or less, based on the total molar number of all the repeating units contained in the particulate polymer being 1. If the molar fraction of the acid group-containing monomer unit in the particulate polymer is within the above range, the heat shrinkage resistance of the obtained heat-resistant layer can be further improved.
[ ethylenically unsaturated Carboxylic acid amide monomer units ]
The ethylenically unsaturated carboxylic acid amide monomer unit is a monomer unit obtained by polymerizing an ethylenically unsaturated carboxylic acid amide monomer. Examples of the ethylenically unsaturated carboxylic acid amide monomer include: acrylamide, methacrylamide, N-methoxymethyl acrylamide, N-methoxymethyl methacrylamide and the like. These may be used alone or in combination of two or more in an arbitrary ratio. Among them, acrylamide and methacrylamide are preferable, and acrylamide is more preferable.
When the particulate polymer contains the ethylenically unsaturated carboxylic acid amide monomer unit, the molar fraction of the ethylenically unsaturated carboxylic acid amide monomer unit in the particulate polymer is preferably 0.01 or more, more preferably 0.02 or more, preferably 0.1 or less, and more preferably 0.08 or less, based on the total molar number of all the repeating units contained in the particulate polymer being 1. If the molar fraction of the ethylenically unsaturated carboxylic acid amide monomer units in the particulate polymer is within the above range, the peel strength of the obtained heat-resistant layer can be further improved.
[ crosslinkable monomer Unit ]
The crosslinkable monomer unit is a structural unit having a structure formed by polymerizing a crosslinkable monomer. The crosslinkable monomer is a monomer which can form a crosslinked structure during or after polymerization when heat or energy ray irradiation is used as a trigger. More specifically, examples of the crosslinkable monomer unit include a crosslinkable group having thermal crosslinking properties and a crosslinkable monomer having 1 ethylenic double bond per 1 molecule (hereinafter, sometimes referred to as "crosslinkable monomer 1"); a crosslinkable monomer having 2 or more ethylenic double bonds per 1 molecule (hereinafter sometimes referred to as "crosslinkable monomer 2"), and the like. These may be used alone or in combination of two or more in an arbitrary ratio. The crosslinkable monomer unit does not include monomer units corresponding to the above-mentioned and various monomer units described later.
Examples of the thermally crosslinkable group that the crosslinkable monomer 1 may contain include an epoxy group, an oxetanyl group, an oxazoline group, and a combination thereof. Specific examples of the crosslinkable group having an epoxy group as a thermal crosslinkable group in the crosslinkable monomer 1 include glycidyl acrylate and glycidyl methacrylate.
Further, examples of the crosslinkable monomer 2 include allyl (meth) acrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, and the like. In addition, in the present specification, (meth) acrylate means acrylate or methacrylate. Among them, allyl (meth) acrylate is preferable, and allyl methacrylate is more preferable.
When the particulate polymer contains a crosslinkable monomer unit, the molar fraction of the crosslinkable monomer unit in the particulate polymer is preferably 0.001 to 0.1, where the total molar number of all the repeating units contained in the particulate polymer is 1. If the molar fraction of the crosslinkable monomer unit in the particulate polymer is within the above range, the cycle characteristics of the obtained secondary battery can be improved.
[ aromatic vinyl monomer Unit ]
The aromatic vinyl monomer unit is a monomer unit obtained by polymerizing an aromatic vinyl monomer. The aromatic vinyl monomer is not particularly limited, and examples thereof include styrene, α -methylstyrene, vinyltoluene, divinylbenzene, and the like. These aromatic vinyl monomers may be used alone or in combination of two or more at an arbitrary ratio. Among them, styrene is preferable as the aromatic vinyl monomer.
When the particulate polymer contains an aromatic vinyl monomer unit, the molar fraction of the aromatic vinyl monomer unit in the particulate polymer is preferably 0.1 to 0.3, based on the total molar number of all the repeating units contained in the particulate polymer being 1. If the mole fraction of the aromatic vinyl monomer unit in the particulate polymer is within the above range, the heat shrinkage resistance of the obtained heat-resistant layer can be improved.
[ fluorine atom-containing monomer Unit ]
The fluorine atom-containing monomer unit is a monomer unit obtained by polymerizing a fluorine atom-containing monomer. Examples of the monomer containing a fluorine atom include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, vinyl trifluoride, vinyl fluoride, perfluoroalkyl vinyl ether, and the like. These may be used alone or in combination of two or more in an arbitrary ratio.
[ aliphatic conjugated diene monomer Unit ]
The aliphatic conjugated diene monomer unit is a monomer unit obtained by polymerizing an aliphatic conjugated diene monomer. Examples of the aliphatic conjugated diene monomer include 1, 3-butadiene, 2-methyl-1, 3-butadiene, 2, 3-dimethyl-1, 3-butadiene, and 2-chloro-1, 3-butadiene. These may be used alone or in combination of two or more in an arbitrary ratio.
Properties
[ parameter MOH/S]
The particulate polymer requires a value M for the mole fraction of hydroxyl-containing monomer units in the particulate polymerOHValue S (μm) divided by the surface area of the particulate polymer2) To the obtained value (M)OH(S) is 0.40 or more. If the parameter MOHWhen the value of/S is 0.40 or more, the peel strength of the obtained heat-resistant layer can be sufficiently improved. Further, from the viewpoint of further improving the balance among the peel strength, heat shrinkage resistance, and cycle characteristics of the obtained heat-resistant layer, the parameter MOHThe value of/S is more preferably 0.45 or more.
[ volume average particle diameter ]
The volume average particle diameter of the particulate polymer is preferably 0.08 μm or more, more preferably 0.10 μm or more, preferably 0.30 μm or less, more preferably 0.25 μm or less, still more preferably 0.20 μm or less, and particularly preferably 0.18 μm or less. If the volume average particle diameter of the particulate polymer is not less than the lower limit, excessive reduction in air permeability of the obtained heat-resistant layer can be suppressed, and the rate characteristics of the obtained secondary battery can be improved. Further, if the volume average particle diameter of the particulate polymer is not more than the above upper limit, the heat shrinkage resistance of the obtained heat-resistant layer can be improved.
The volume average particle diameter of the particulate polymer can be adjusted by, for example, changing the kind and amount of the monomer, polymerization initiator and/or polymerization accelerator used for producing the particulate polymer.
[ degree of swelling in electrolyte ]
The swelling degree of the particulate polymer in the electrolyte is preferably 8.0 times or less, more preferably 4.5 times or less, further preferably 4.2 times or less, and particularly preferably 4.0 times or less. The swelling degree of the particulate polymer in the electrolyte is usually more than 1.0 times, and preferably 1.5 times or more. If the degree of swelling of the particulate polymer is not more than the above upper limit, the cycle characteristics of the obtained secondary battery can be improved. Further, when the swelling degree of the particulate polymer satisfies the lower limit, the rate characteristics of the obtained secondary battery can be improved.
Process for producing granular Polymer
Here, the method of polymerizing the particulate polymer is not particularly limited, and any of solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, and the like can be used. Further, as the polymerization reaction, addition polymerization such as ionic polymerization, radical polymerization, living radical polymerization, and the like can be used. In addition, as the polymerization solvent, emulsifier, dispersant, polymerization initiator, chain transfer agent and the like which can be used for the polymerization, usual ones can be used, and the amount thereof can be the amount which is usually used.
In the binder composition of the present invention, the content of the particulate polymer is not particularly limited.
< dispersing Medium >
Examples of the dispersion medium that may be optionally contained in the binder composition of the present invention include water, organic solvents (for example, esters, ketones, alcohols), and mixtures thereof. The adhesive composition of the present invention may contain one kind of organic solvent, or may contain two or more kinds of organic solvents. Among them, water is preferable as the dispersion medium.
< other ingredients >
The adhesive composition of the present invention may contain: water-soluble polymers, reinforcing materials, leveling agents, wetting agents, dispersing agents, viscosity regulators, electrolyte additives, preservatives, mildewcides, antifoaming agents, polymerization inhibitors, and binding materials other than the above granular polymers. These other components are not particularly limited as long as they do not affect the battery reaction, and known components can be used. In addition, one kind of the other component may be used alone, or two or more kinds may be used in combination at an arbitrary ratio.
The water-soluble polymer that can be optionally contained in the binder composition for a heat-resistant layer of a nonaqueous secondary battery is a component that functions as a viscosity modifier in the binder composition and a slurry composition containing the binder composition.
The term "water-soluble" as used herein means that the insoluble matter is less than 1.0% by mass when 0.5g of the polymer is dissolved in 100g of water at a temperature of 25 ℃.
The water-soluble polymer is not particularly limited, and various thickening polysaccharides can be used. As the thickening polysaccharide, carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, polyvinyl alcohol, polyacrylic acid, or salts thereof are preferably used, and carboxymethyl cellulose or salts thereof are particularly preferably used.
Examples of the carboxymethyl cellulose salt include sodium salt and ammonium salt. The thickening polysaccharides may be used alone, or two or more thereof may be used in combination at an arbitrary ratio.
The wetting agent that can be optionally contained in the binder composition for a heat-resistant layer of a nonaqueous secondary battery is not particularly limited, and an ethylene oxide/propylene oxide surfactant (EO/PO surfactant), a fluorine surfactant, a silicon surfactant, and the like can be used. Among these, EO/PO surfactants and fluorine surfactants are preferably used, and EO/PO surfactants are more preferably used.
The dispersant is not particularly limited, and polycarboxylic acids such as polyacrylic acid, sodium polycarboxylates such as sodium polyacrylate, ammonium polycarboxylates such as ammonium polyacrylate, polycarboxylic acid sulfonic acid copolymers, polycarboxylic acid sulfonic acid copolymer sodium, polycarboxylic acid sulfonic acid copolymer ammonium, and the like can be used. Among them, sodium polyacrylate is preferably used.
Specific examples of the components other than the wetting agent and the dispersant are not particularly limited, and examples thereof include those described in international publication No. 2012/115096.
< preparation of Binder composition for Heat-resistant layer of nonaqueous Secondary Battery >
Further, the binder composition of the present invention can be prepared by mixing the above particulate polymer with any other component as necessary by a known method. Specifically, the binder composition can be prepared by mixing the above-described respective ingredients using a mixer such as a ball mill, a sand mill, a bead mill, a pigment dispersing machine, an attritor, an ultrasonic dispersing machine, a homogenizer, a planetary mixer, a Filmix, or the like.
In addition, for example, in the case of producing a particulate polymer by polymerization in an aqueous solution, the particulate polymer can be used as it is as a binder composition in the state of an aqueous dispersion of the particulate polymer.
(slurry composition for nonaqueous Secondary Battery Heat-resistant layer)
The slurry composition of the present invention is a composition for use in forming a heat-resistant layer, and contains the non-conductive inorganic particles and the above-described binder composition, and optionally other components. That is, the slurry composition of the present invention generally contains the non-conductive particles, the particulate polymer, and the dispersion medium, and optionally other components. Further, since the slurry composition of the present invention contains the binder composition, a heat-resistant layer having a sufficiently high peel strength can be formed.
< non-conductive particles >
Here, the nonconductive particles contained in the slurry composition for a heat-resistant layer are not particularly limited, and include particles made of an inorganic material (i.e., nonconductive inorganic particles) and particles made of an organic material (i.e., nonconductive organic particles) that are stable in the use environment of the secondary battery, are electrochemically stable, and are stable. Among them, non-conductive inorganic particles are preferable. When preferred examples of the non-conductive inorganic particles are mentioned, there may be mentioned: alumina (aluminum, Al)2O3) Aluminum oxide hydrate (boehmite, AlOOH), gibbsite (Al (OH)3) Silicon oxide, magnesium oxide (magnesia), magnesium hydroxide, calcium oxide, titanium oxide (Titania), barium titanate (BaTiO)3) Inorganic oxide particles such as ZrO and alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystal particles of silicon, diamond, or the like; insoluble ionic crystal particles such as barium sulfate, calcium fluoride, barium fluoride and the like; clay fine particles such as talc and montmorillonite. Among these, from the viewpoint of improving the adhesion between the heat-resistant layer and the substrate, the non-conductive particles are preferably particles composed of alumina (alumina particles), particles composed of boehmite (boehmite particles), particles composed of titanium oxide (titanium oxide particles), and particles composed of barium sulfate (barium sulfate particles), more preferably alumina particles, boehmite particles, and barium sulfate particles, and still more preferably alumina particles and barium sulfate particles.
These particles may be subjected to element substitution, surface treatment, solution treatment, or the like as necessary. These particles may be used alone or in combination of two or more.
In addition, the non-conductive organic particles are organic compounds different from the particulate polymer as the binder. That is, the non-conductive organic particles do not have cohesiveness. Preferable examples of the non-conductive organic particles include crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, crosslinked styrene-divinylbenzene copolymer, polystyrene, polyimide, polyamide, polyamideimide, melamine resin, phenol resin, and benzoguanamine-formaldehyde condensate, and heat-resistant polymer particles such as polysulfone, polyacrylonitrile, polyaramide, polyacetal, and thermoplastic polyimide. Further, as the non-conductive organic particles, modified products and derivatives thereof can also be used. These particles may be used alone or in combination of two or more.
The glass transition temperature of the organic particles as the nonconductive particles is preferably more than 20 ℃, and usually 350 ℃ or less. The glass transition temperature of the organic particles can be measured according to JIS K7121.
The volume average particle diameter of the nonconductive particles is preferably 0.7 μm or less, more preferably 0.5 μm or less, and further preferably 0.4 μm or less. If the volume average particle diameter of the non-conductive particles is not more than the above upper limit, the heat shrinkage resistance of the obtained heat-resistant layer can be improved. The volume average particle diameter of the nonconductive particles may be usually 0.05 μm or more. The volume average particle diameter of the nonconductive particles can be measured by applying a laser analysis method according to JIS Z8825 to the nonconductive particles pretreated according to JIS Z8824.
< Binder composition >
As the adhesive composition, the adhesive composition of the present invention described above is used.
In addition, from the viewpoint of suppressing excessive decrease in air permeability of the obtained heat-resistant layer, the content of the predetermined particulate polymer in the slurry composition is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and further preferably 6 parts by mass or less in terms of solid content, relative to 100 parts by mass of the non-conductive particles. From the viewpoint of further improving the peel strength of the obtained heat-resistant layer, the content of the predetermined particulate polymer in the slurry composition is preferably 1 part by mass or more, more preferably 1.2 parts by mass or more, and still more preferably 1.5 parts by mass or more, in terms of solid content, relative to 100 parts by mass of the non-conductive particles. When the slurry composition contains a water-soluble polymer as an optional component described later, the content of the particulate polymer is preferably higher than the content of the water-soluble polymer.
< other ingredients >
The other components that can be blended in the slurry composition are not particularly limited, and the same components as those that can be blended in the binder composition of the present invention can be exemplified. In addition, one kind of the other component may be used alone, or two or more kinds may be used in combination at an arbitrary ratio.
From the viewpoint of further improving the heat shrinkage resistance of the obtained heat-resistant layer, the content of the water-soluble polymer as an optional component in the slurry composition is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, in terms of solid content, relative to 100 parts by mass of the non-conductive particles (particularly, the non-conductive inorganic particles). From the viewpoint of suppressing excessive decrease in air permeability of the obtained heat-resistant layer, the content of the water-soluble polymer as an optional component in the slurry composition is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, in terms of solid content, relative to 100 parts by mass of the non-conductive particles (particularly, the non-conductive inorganic particles).
The content of the wetting agent as an optional component in the slurry composition is preferably 0.01 part by mass or more, preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and further preferably 1 part by mass or less with respect to 100 parts by mass of the non-conductive particles (particularly, the non-conductive inorganic particles). When the content of the wetting agent is not less than the lower limit, the peel strength of the obtained heat-resistant layer can be further improved. Further, if the content of the wetting agent is not more than the above upper limit, the cycle characteristics of the secondary battery can be improved.
Further, the content of the dispersant as an optional component in the slurry composition is preferably 0.1 part by mass or more, preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and further preferably 1 part by mass or less, relative to 100 parts by mass of the non-conductive particles (particularly, the non-conductive inorganic particles). When the content of the dispersant is not less than the lower limit, the heat shrinkage resistance of the heat-resistant layer can be improved. Further, if the content of the dispersant is not more than the above upper limit, the cycle characteristics of the secondary battery can be improved.
< preparation of slurry composition for heat-resistant layer of nonaqueous Secondary Battery >
The slurry composition can be prepared by mixing the above components by a known mixing method described in the section < preparation of binder composition for heat-resistant layer of nonaqueous secondary battery >.
(Heat-resistant layer for nonaqueous Secondary Battery)
The heat-resistant layer of the present invention is formed from the slurry composition of the present invention, and can be formed by, for example, applying the slurry composition to a suitable substrate surface to form a coating film and then drying the formed coating film. That is, the heat-resistant layer of the present invention is formed from a dried product of the slurry composition, and usually contains at least nonconductive particles and a particulate polymer. Since each component contained in the heat-resistant layer is each component contained in the slurry composition, the preferred presence ratio of each component is the same as the preferred presence ratio of each component in the slurry composition.
Further, the heat-resistant layer of the present invention is formed from the slurry composition of the present invention containing the binder composition of the present invention, and therefore, the peel strength is sufficiently high.
< substrate >
Here, the substrate to which the slurry composition is applied is not limited, and for example, a coating film of the slurry composition may be formed on the surface of the release substrate, the coating film may be dried to form a heat-resistant layer, and the release substrate may be peeled from the heat-resistant layer. In this manner, the heat-resistant layer peeled from the release substrate can be used as a self-supporting film for forming a battery member of a secondary battery.
However, from the viewpoint of omitting the step of peeling off the heat-resistant layer to improve the production efficiency of the battery member, it is preferable to use a spacer substrate or an electrode substrate as the substrate. Specifically, the paste composition is preferably coated on the spacer substrate or the electrode substrate, more preferably on the spacer substrate.
Spacer substrate
The spacer base material is not particularly limited, and known spacer base materials such as organic spacer base materials can be mentioned. The organic separator substrate is a porous member formed of an organic material, and examples of the organic separator substrate include a microporous film and a nonwoven fabric made of a polyolefin resin such as polyethylene and polypropylene, an aromatic polyamide resin, and the like. From the viewpoint of excellent strength, a microporous film or nonwoven fabric made of polyethylene is preferable.
Electrode base Material
The electrode base (positive electrode base and negative electrode base) is not particularly limited, and examples thereof include an electrode base in which an electrode composite material layer containing an electrode active material and a binder is formed on a current collector.
Known methods can be used for the current collector, the electrode active material (positive electrode active material, negative electrode active material) and the binder for the electrode composite material layer (binder for the positive electrode composite material layer, binder for the negative electrode composite material layer) in the electrode composite material layer, and the method for forming the electrode composite material layer on the current collector, and examples thereof include the method described in japanese patent application laid-open No. 2013-145763.
< method for forming heat-resistant layer >
As a method for forming a heat-resistant layer on a substrate such as the above-mentioned spacer substrate or electrode substrate, the following methods can be mentioned.
1) A method in which the slurry composition of the present invention is applied to the surface of a substrate (in the case of an electrode substrate, the surface on the electrode composite layer side, the same applies hereinafter) and then dried;
2) a method of immersing a substrate in the slurry composition of the present invention and then drying it; and
3) a method of producing a heat-resistant layer by applying the slurry composition of the present invention to a release substrate, drying the applied composition, and transferring the obtained heat-resistant layer to the surface of the substrate.
Among these, the method of 1) is particularly preferable in terms of easy control of the layer thickness of the heat-resistant layer. The method of 1) above specifically includes a step of applying the slurry composition to the base material (application step) and a step of drying the slurry composition applied to the base material to form the heat-resistant layer (drying step).
Coating Process
In the coating step, the method of coating the slurry composition on the substrate is not particularly limited, and examples thereof include a doctor blade method, a reverse roll method, a direct roll method, an gravure method, an extrusion method, a brush coating method, and the like.
Drying Process
In the drying step, a method for drying the slurry composition on the base material is not particularly limited, and a known method can be used. Examples of the drying method include drying with warm air, hot air, or low-humidity air; vacuum drying; drying by irradiation with infrared rays, electron beams, or the like.
< thickness of Heat-resistant layer >
The thickness of the heat-resistant layer is preferably 4 μm or less, more preferably 3 μm or less, still more preferably 2.5 μm or less, and particularly preferably 2 μm or less. The thickness of the heat-resistant layer is not particularly limited, and may be, for example, 0.2 μm or more. If the thickness of the heat-resistant layer is not more than the above upper limit, the cycle characteristics of the obtained secondary battery can be improved. Further, if the thickness of the heat-resistant layer is not less than the above lower limit value, the heat-resistant layer is excellent in heat shrinkage resistance.
(nonaqueous Secondary Battery)
The secondary battery of the present invention has the above-described heat-resistant layer of the present invention. More specifically, the secondary battery of the present invention has a positive electrode, a negative electrode, a separator, and an electrolytic solution, and the above-described heat-resistant layer is contained in at least one of the positive electrode, the negative electrode, and the separator as a battery member.
< Positive electrode, negative electrode and separator >
At least one of the positive electrode, the negative electrode, and the separator used in the secondary battery of the present invention is a battery member having the heat-resistant layer of the present invention. The positive electrode, the negative electrode, and the separator that do not have the heat-resistant layer of the present invention are not particularly limited, and known positive electrodes, negative electrodes, and separators can be used.
< electrolyte >
As the electrolyte, it is usually used in an organic solventThe agent dissolves an organic electrolyte solution supporting the electrolyte. As the supporting electrolyte, a lithium salt can be used in, for example, a lithium ion secondary battery. Examples of the lithium salt include: LiPF6、LiAsF6、LiBF4、LiSbF6、LiAlCl4、LiClO4、CF3SO3Li、C4F9SO3Li、CF3COOLi、(CF3CO)2NLi、(CF3SO2)2NLi、(C2F5SO2) NLi, etc. Among these, LiPF is preferable because it is easily soluble in a solvent and exhibits a high dissociation degree6、LiClO4、CF3SO3And Li. The electrolyte may be used alone or in combination of two or more. In general, since the lithium ion conductivity tends to be higher when a supporting electrolyte having a higher dissociation degree is used, the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.
The organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte, and in a lithium ion secondary battery, for example, alkyl carbonates such as dimethyl carbonate (DMC), Ethylene Carbonate (EC), diethyl carbonate (DEC), Propylene Carbonate (PC), Butylene Carbonate (BC), and Ethyl Methyl Carbonate (EMC); esters such as γ -butyrolactone and methyl formate; ethers such as 1, 2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide, and the like. Further, a mixed solution of these solvents may also be used. Among them, carbonates are preferable because of high dielectric constant and wide stable potential region.
In addition, the concentration of the electrolyte in the electrolytic solution can be appropriately adjusted. In addition, known additives such as Vinylene Carbonate (VC) may be added to the electrolyte.
< method for producing nonaqueous secondary battery >
The nonaqueous secondary battery of the present invention can be produced, for example, by: the positive electrode and the negative electrode are stacked with a separator interposed therebetween, and the stack is wound, folded, or the like into a battery container according to the battery shape as needed, and an electrolyte solution is injected into the battery container and sealed. At least one of the positive electrode, the negative electrode, and the separator is a member with a heat-resistant layer. In order to prevent the pressure inside the secondary battery from rising, the occurrence of overcharge and discharge, etc., overcurrent prevention elements such as fuses and PTC elements, expanded metal, guide plates, etc., may be provided as necessary. The shape of the secondary battery may be any of coin, button, sheet, cylinder, square, flat, and the like, for example.
Examples
The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the following description, "%" and "part" of the amounts are based on mass unless otherwise specified.
In addition, unless otherwise specified, in a polymer produced by polymerizing a plurality of monomers, the proportion (or mole fraction) of a monomer unit in the polymer formed by polymerizing a certain monomer is generally equal to the ratio (charge ratio or mole fraction) of the certain monomer to the total monomers used for polymerization of the polymer. Further, the measurement and evaluation of various properties in examples and comparative examples were carried out in accordance with the following methods.
< volume average particle diameter of particulate Polymer >
The volume average particle diameter of the particulate polymers prepared in examples and comparative examples was measured by a laser diffraction method. Specifically, an aqueous dispersion (solid content concentration adjusted to 0.1 mass%) containing the object to be measured (particulate polymer) was used as a sample. Then, in a particle size distribution (volume basis) measured by a laser diffraction type particle size distribution measuring apparatus (product name "LS-13320" manufactured by Beckman Coulter corporation), a particle size D50 in which a cumulative volume calculated from a small particle size side reaches 50% was defined as a volume average particle size.
< parameter MOH/S＞
With respect to the granular polymers prepared in examples and comparative examples, the value M of the mole fraction of the hydroxyl group-containing monomer unit in the granular polymer was calculated according to the following formulaOHValue S (μm) divided by the surface area of the particulate polymer2) To the obtained value (M)OH/S)。
MOH(value of mole fraction of hydroxyl group-containing monomer units in particulate polymer M)OH) [ mu ] m of (4 π X (volume average particle diameter of particulate polymer/2))2)
Further, the value M as the mole fraction of the hydroxyl group-containing monomer unitOHThe mole fraction of hydroxyl group-containing monomer in the monomer composition used in the preparation of each particulate polymer is used. In addition, the mole fractions of other various monomer units are also related to MOHThe values of (A) are calculated in the same manner and shown in Table 1.
Further, as described in the above formula, the value S (μm) of the surface area of the particulate polymer as the particulate polymer2) The shape of the granular polymer was simulated as a regular sphere, and the volume average particle diameter D50 obtained as above was used.
< swelling degree in electrolyte >
The granular polymers prepared in examples and comparative examples were formed into films having a thickness of about 0.1mm, cut out in a square of about 2cm to obtain test pieces, and the mass of the test pieces (mass before immersion) was measured. Thereafter, the test piece was immersed in the electrolyte solution at a temperature of 60 ℃ for 72 hours. The immersed test piece was pulled up, the electrolyte solution was wiped off, the mass (mass after immersion) was immediately measured, and the value of (mass after immersion)/(mass before immersion) was defined as the swelling degree.
Further, as the electrolyte, a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a mass ratio of 3: 7 (in which LiPF is dissolved at a concentration of 1 mol/L) was used6And (3) obtaining a solution. The smaller the value of the obtained swelling degree, the higher the electrolyte resistance of the particulate polymer.
< Water solubility of particulate Polymer >
The granular polymers prepared in examples and comparative examples were dissolved in 100g of water at 25 ℃ to obtain 0.5g of the polymer. It was confirmed that the insoluble content in all examples and comparative examples was 90% by mass or more.
< adhesion of Heat-resistant layer for nonaqueous Secondary Battery >
The heat-resistant layer-equipped spacers produced in examples and comparative examples were cut into pieces having a width of 10mm and a length of 50mm, respectively, to produce test pieces.
Next, a sus (solid steel) plate to which a double-sided tape (No. 5608 made by NITTO DENKO CORPORATION) was attached was prepared, and the heat-resistant layer side surface of the test piece was attached to the double-sided tape. Then, one end of the spacer base material was pulled at a speed of 50 mm/min so that the peel plane became 180 °, and the peel strength at the time of peeling was measured and evaluated according to the following criteria. Higher peel strength means higher adhesion between the spacer base material and the heat-resistant layer.
A: peel strength of 50N/m or more
B: a peel strength of 30N/m or more and less than 50N/m
C: peel strength less than 30N/m
< Heat shrinkage resistance of Heat-resistant layer for nonaqueous Secondary Battery >
The heat-resistant layer-equipped spacers produced in examples and comparative examples were cut into squares having a width of 12cm × a length of 12cm, and a square having 10cm sides at 1 side was drawn inside the squares to prepare test pieces. Then, the test piece was placed in a thermostatic bath at 150 ℃ and left to stand for 1 hour, and then the change in the area of the square drawn inside ({ (area of square before left to stand-area of square after left to stand)/area of square before left to stand } × 100%) was determined as the thermal shrinkage rate, and evaluated according to the following criteria. A smaller heat shrinkage ratio indicates a more excellent heat shrinkage resistance of the heat-resistant layer.
A: the thermal shrinkage is less than 10%
B: the thermal shrinkage rate is more than 10 percent and less than 20 percent
C: a heat shrinkage of 20% or more
< cycle characteristics of nonaqueous Secondary Battery >
The lithium ion secondary batteries fabricated in examples and comparative examples were allowed to stand at 25 ℃ for 24 hours. Then, the initial capacity C0 was measured by charging to 4.2V at a constant voltage and constant current (CC-CV) at a charge rate of 1C (cut-off condition: 0.02C) and discharging to 3.0V at a discharge rate of 1C and Constant Current (CC) at 25 ℃.
Further, the same charge and discharge operations were repeated in an environment of 25 ℃, and the capacity C1 after 300 cycles was measured. Then, the capacity retention rate Δ C was calculated as (C1/C0) × 100 (%), and evaluated according to the following criteria. The higher the value of the capacity retention rate, the less the decrease in the discharge capacity, and the more excellent the cycle characteristics.
A: the capacity retention rate Delta C is more than 85%
B: the capacity retention rate Delta C is more than 75 percent and less than 85 percent
C: the capacity retention rate delta C is less than 75 percent
(example 1)
Preparation of an aqueous Dispersion comprising particulate Polymer A
In a reactor equipped with a stirrer, 90 parts of ion exchange water, 0.05 part of sodium dodecylbenzenesulfonate ("Neopelex G-15" manufactured by Kao Chemicals Corporation) as an emulsifier, and 0.23 part of ammonium persulfate were supplied, and the gas phase portion was replaced with nitrogen gas and the temperature was raised to 70 ℃.
On the other hand, in another vessel, 50 parts of ion exchange water, 0.1 part of sodium dodecylbenzenesulfonate as AN emulsifier, 2.2 parts of Acrylonitrile (AN) as a cyano group-containing monomer, 2.5 parts of N-methylolacrylamide (NMA) as a hydroxyl group-containing monomer, and 92.0 parts of N-Butyl Acrylate (BA) as other monomers, 2.1 parts of methacrylic acid (MAA), and 1.2 parts of acrylamide (AAm) were mixed to obtain a monomer composition. The monomer composition was continuously added to the above-mentioned reactor over 4 hours to conduct polymerization. During the addition, the reaction was carried out at 80 ℃. After the addition was completed, the mixture was further stirred at 80 ℃ for 3 hours to complete the reaction, thereby producing an aqueous dispersion (a binder composition for a heat-resistant layer) containing the particulate polymer a. The volume average particle diameter and the parameter M of the resulting particulate polymer A were measured or calculated as described aboveOH(ii) S and the degree of swelling in the electrolyte. The results are shown in Table 1. The obtained particulate polymer a was a (meth) Acrylate Copolymer (ACL) having a mole fraction of n-butyl acrylate units as acrylate monomer units of 0.87.
< preparation of slurry composition for Heat-resistant layer >
Alumina particles (0.3 μm in volume average particle diameter D50 (catalog value) manufactured by Sumitomo Chemical Co. Ltd.) were used as the nonconductive particles, sodium polyacrylate (Toa Gosei Co., manufactured by Ltd., Aron T-50) was used as the dispersant, and carboxymethylcellulose (D1220 manufactured by Daicel Fine Chem Ltd.) having an etherification degree of 0.8 to 1.0 was used as the water-soluble polymer. The viscosity of a 1% aqueous solution of the water-soluble polymer is 10 to 20 mPas.
100 parts of the nonconductive particles, 0.5 part of the dispersant, and ion-exchanged water were mixed and treated with a bead mill (manufactured by Ashizawa Finetech ltd., LMZ015) for 1 hour to obtain a dispersion. Further, the binder composition for a heat-resistant layer prepared as described above was mixed in an amount of 4 parts by solid equivalent of the particulate polymer a, 1.5 parts by solid equivalent of a 4% aqueous solution of carboxymethyl cellulose, and 0.3 part by weight of an ethylene oxide/propylene oxide surfactant (manufactured by SanNopco Limited, Noptex ED-052) as a wetting agent to prepare a slurry composition for a heat-resistant layer having a solid content concentration of 40 mass%.
< production of heat-resistant layer-equipped spacer having heat-resistant layer on one side >
A polyethylene spacer substrate (manufactured by Asahi Kasei Corporation, ND509, thickness: 9 μm) was prepared. The prepared slurry composition for a heat-resistant layer was applied to the surface of the prepared spacer base material, and dried at 50 ℃ for 3 minutes to obtain a heat-resistant layer-equipped spacer (thickness of heat-resistant layer: 2 μm) having a heat-resistant layer on one surface. Using the obtained heat-resistant layer-equipped spacer, the adhesion and heat shrinkage resistance of the heat-resistant layer were evaluated by the above evaluation methods. The results are shown in Table 1.
< production of negative electrode >
First, 33 parts of 1, 3-butadiene, 3.5 parts of itaconic acid, 63.5 parts of styrene, 0.4 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate as a polymerization initiator were charged into a 5MPa pressure-resistant vessel equipped with a stirrer, and after sufficient stirring, the mixture was heated to 50 ℃ to initiate polymerization. When the polymerization conversion rate reached 96%, the mixture was cooled to terminate the polymerization reaction, thereby obtaining a mixture containing a granular binder (styrene-butadiene copolymer). To the above mixture was added a 5% aqueous solution of sodium hydroxide, the pH was adjusted to 8, and then unreacted monomers were removed by distillation under reduced pressure by heating. Thereafter, the mixture was cooled to 30 ℃ or lower to obtain an aqueous dispersion containing the binder for a negative electrode.
48.75 parts of artificial graphite (theoretical capacity: 360mAh/g) and 48.75 parts of natural graphite (theoretical capacity: 360mAh/g) as negative electrode active materials, and 1 part of carboxymethyl cellulose as a thickener in terms of solid content equivalent were put into a planetary mixer. Further, the resulting mixture was diluted with ion-exchanged water to a solid content concentration of 60%, and kneaded at a rotation speed of 45rpm for 60 minutes. Thereafter, 1.5 parts by solid equivalent of the binder for a negative electrode obtained as described above was charged and kneaded at 40rpm for 40 minutes. Then, ion-exchanged water was added so that the viscosity became 3000. + -.500 mPas (measured at 25 ℃ C. and 60 rpm) to prepare a slurry composition for a negative electrode composite material layer.
Coating the slurry composition for the negative electrode composite material layer by a corner cut wheel coater in an amount of 11 + -0.5 mg/cm2The method (2) was applied to the surface of a copper foil having a thickness of 15 μm as a current collector. Thereafter, the copper foil coated with the slurry composition for a negative electrode composite layer was conveyed at a speed of 400 mm/min for 2 minutes in an oven at a temperature of 80 ℃ and further for 2 minutes in an oven at a temperature of 110 ℃ to dry the slurry composition on the copper foil, thereby obtaining a negative electrode material having a negative electrode composite layer formed on a current collector.
Then, the negative electrode composite layer side of the produced negative electrode material was rolled under a condition of a linear pressure of 11t (ton) at an environment of 25. + -. 3 ℃ to obtain a negative electrode composite layer having a density of 1.60g/cm3The negative electrode of (1). Thereafter, the negative electrode was left to stand at a temperature of 25. + -. 3 ℃ and a relative humidity of 50. + -. 5% for 1 week.
< production of Positive electrode >
96 parts of a lithium complex oxide-based active material (NMC111, LiNi) of Co-Ni-Mn as a positive electrode active material was added to a planetary mixer1/3Co1/3Mn1/3O2) 2 parts of acetylene black (Denka co., ltd., product name "HS-100") as a conductive material, 2 parts of polyvinylidene fluoride (KF-1100) as a binder, and N-methyl-2-pyrrolidone (NMP) as a dispersion medium were added to make the total solid content concentration 67%, and mixed to prepare a slurry composition for a positive electrode composite material layer.
Next, the obtained slurry composition for a positive electrode composite material layer was applied in an amount of 20. + -. 0.5mg/cm by a comma coater2Is applied to an aluminum foil having a thickness of 20 μm as a current collector.
Further, the slurry composition on the aluminum foil was dried by conveying the slurry composition at a speed of 200 mm/min for 2 minutes in an oven at a temperature of 90 ℃ and further for 2 minutes in an oven at a temperature of 120 ℃ to obtain a positive electrode material having a positive electrode composite layer formed on a current collector.
Then, the positive electrode material was rolled under a condition of a linear pressure of 14t (ton) at an atmosphere of 25. + -. 3 ℃ to the positive electrode composite layer side of the produced positive electrode material to obtain a positive electrode composite layer having a density of 3.40g/cm3The positive electrode of (1). Thereafter, the positive electrode was left to stand at a temperature of 25. + -. 3 ℃ and a relative humidity of 50. + -. 5% for 1 week.
< production of Secondary Battery >
Using the negative electrode, the positive electrode, and the separator, a wound battery cell (discharge capacity equivalent to 520mAh) was prepared and disposed in an aluminum packaging material. Then, LiPF was filled in the aluminum packaging material as an electrolyte at a concentration of 1.0M6A solution (a mixed solvent of Ethylene Carbonate (EC)/Ethyl Methyl Carbonate (EMC) 3/7 (mass ratio) as a solvent, and an additive containing vinylene carbonate at 2 vol% (solvent ratio)). Further, in order to seal the opening of the aluminum packaging material, heat sealing at a temperature of 150 ℃ was performed to seal the aluminum packaging material, thereby producing a lithium ion secondary battery. The lithium ion secondary battery was used to evaluate cycle characteristics. The results are shown in Table 1.
(examples 2 to 7, 9 and 11)
Various operations, measurements and evaluations were carried out in the same manner as in example 1 except that, when the particulate polymer was synthesized, the composition of the monomer composition used for polymerization and the like were changed as needed, and the types, mole fractions, particle diameters and degrees of swelling in the electrolytic solution of the various monomer units in the obtained particulate polymer were respectively shown in table 1. The results are shown in Table 1.
In table 1, the particulate polymers having compositions and the like different from those of example 1, which were prepared in these examples, are referred to as particulate polymers B to G, H, J, respectively.
In table 1, the columns showing the kind and mole fraction of the hydroxyl group-containing monomer unit in examples 7 and 10 are denoted as "NMA/. beta. -HEA" and "0.03/0.05", respectively. The expression "NMA/β -HEA" as a class means that the particulate polymer contains both N-methylolacrylamide units and β -hydroxyethyl acrylate units, and the expression "0.03/0.05" as a molar fraction means that the molar fraction of N-methylolacrylamide units is 0.03 and the molar fraction of β -hydroxyethyl acrylate units is 0.05.
(example 8)
Various operations, measurements and evaluations were carried out in the same manner as in example 1 except that in the step of "preparation of slurry composition for heat-resistant layer", the non-conductive particles used were changed from alumina particles to barium sulfate particles (Takehara Kagaku Kogyo Co., Ltd., TS-2, volume average particle diameter D50 (table value): 0.3 μm). The results are shown in Table 1.
(example 10)
In synthesizing the particulate polymer I, the polymerization conditions were changed from those in the production of the particulate polymer G in example 7 (specifically, the amount of the emulsifier to be fed into the reactor was changed to 0.02 part). In addition to this point, various operations, measurements and evaluations were carried out in the same manner as in example 7. The results are shown in Table 1.
(example 12)
Various operations, measurements and evaluations were carried out in the same manner as in example 1 except that alumina particles having a larger particle diameter (AKP-3000, volume average particle diameter D50 (index value): 0.7 μm, manufactured by Sumitomo Chemical Co. Ltd.) were used as the nonconductive particles in the step of < preparation of slurry composition for heat-resistant layer >. The results are shown in Table 1.
Comparative example 1
The composition of the monomer composition and the like in the synthesis of the particulate polymer are changed as necessary so that the parameter M of the resulting particulate polymer is changedOHVarious operations, measurements and evaluations were carried out in the same manner as in example 1, except that the value of/S was less than 0.4. The results are shown in Table 1. In table 1, the particulate polymer produced in this comparative example is referred to as particulate polymer K.
Comparative example 2
Various operations, measurements and evaluations were carried out in the same manner as in example 1, except that the composition of the monomer composition and the like in synthesizing the particulate polymer were changed as needed so that the resulting particulate polymer did not contain a cyano group-containing monomer unit. The results are shown in Table 1. In table 1, the particulate polymer produced in this comparative example is referred to as particulate polymer L.
Comparative example 3
The composition of the monomer composition and the like in the synthesis of the particulate polymer are changed as necessary so that the resulting particulate polymer does not contain a hydroxyl group-containing monomer unit and it is clear that the parameter M of the resulting particulate polymer isOHVarious operations, measurements and evaluations were carried out in the same manner as in example 1, except that the value of/S was 0. The results are shown in Table 1. In table 1, the particulate polymer produced in this comparative example is referred to as particulate polymer M.
Comparative example 4
Preparation of an aqueous Dispersion containing particulate Polymer N
In a reactor equipped with a stirrer, 70 parts of ion-exchanged water, 0.15 part of sodium lauryl sulfate ("Emal 2F" manufactured by Kao Corporation) as an emulsifier, and 0.5 part of ammonium persulfate were supplied, and the gas phase portion was replaced with nitrogen gas, and the temperature was raised to 60 ℃.
On the other hand, 50 parts of ion exchange water, 0.5 part of sodium dodecylbenzenesulfonate as an emulsifier, 1.2 parts of N-methylolacrylamide as a hydroxyl group-containing monomer, 2 parts of acrylonitrile as a cyano group-containing monomer, and 93.8 parts of N-butyl acrylate as another monomer, 2 parts of methacrylic acid, and 1 part of allyl glycidyl ether were added to another vessel, and further 0.15 part of a chelating agent ("CHELEST 400G" (sodium ethylenediaminetetraacetate tetrahydrate) made by cheelest CORPORATION was mixed to obtain a monomer composition. The monomer composition was continuously added to the above-mentioned reactor over 4 hours to conduct polymerization. During the addition, the reaction was carried out at 60 ℃. After the addition was completed, the reaction was further completed after stirring at 70 ℃ for 3 hours, thereby producing an aqueous dispersion (binder composition for heat-resistant layer) containing the particulate polymer N.
< preparation of slurry composition for heat-resistant layer > < production of secondary battery >
Various operations, measurements, and evaluations were carried out in the same manner as in example 1 except that the binder composition for a heat-resistant layer obtained as described above was used. The results are shown in Table 1.
In addition, in Table 1 shown below,
"AN" represents AN acrylonitrile unit,
"NMA" represents N-methylolacrylamide units,
"BA" represents an n-butyl acrylate unit,
"MAA" represents a methacrylic acid unit,
"Aam" represents an acrylamide unit,
"CMC" means carboxymethyl cellulose,
"beta-HEA" means a beta-hydroxyethyl acrylate unit,
"AMA" represents an allyl methacrylate unit,
"HEMA" represents a hydroxyethyl methacrylate unit,
"MAN" represents a methacrylonitrile unit,
"2 EHA" represents a 2-ethylhexyl acrylate unit,
"St" represents a styrene unit,
"AGE" means an allyl glycidyl ether unit,
“Al2O3"denotes oxidationAluminum particles,
“BaSO4"indicates barium sulfate particles.
[ Table 1]
Figure BDA0003374534600000281
As is clear from Table 1, the resin composition using a resin composition containing a monomer unit having a cyano group and a monomer unit having a hydroxyl group and further containing a predetermined parameter MOHIn examples 1 to 12 of the binder compositions of granular polymers having an S value of 0.40 or more, heat-resistant layers having sufficiently high peel strength and exhibiting high adhesion to the substrate were obtained. In addition, it is understood that the heat-resistant layers of examples 1 to 12 can provide excellent cycle characteristics to the secondary battery.
On the other hand, it is found that the composition contains at least one of a monomer unit having no cyano group and a monomer unit having a hydroxyl group and/or a predetermined parameter MOHIn comparative examples 1 to 4 of the binder compositions of granular polymers having an S value of less than 0.40, the heat-resistant layer having sufficiently high peel strength could not be formed, and the adhesion of the heat-resistant layer to the substrate was insufficient.
Industrial applicability
According to the present invention, it is possible to provide a binder composition for a heat-resistant layer of a nonaqueous secondary battery, which can prepare a slurry composition for a heat-resistant layer of a nonaqueous secondary battery capable of forming a heat-resistant layer for a nonaqueous secondary battery having sufficiently high peel strength.
Further, according to the present invention, it is possible to provide a slurry composition for a heat-resistant layer of a nonaqueous secondary battery, which can form a heat-resistant layer for a nonaqueous secondary battery having sufficiently high peel strength.
Further, according to the present invention, it is possible to provide a heat-resistant layer for a nonaqueous secondary battery having sufficiently high peel strength, and a nonaqueous secondary battery having the heat-resistant layer.

Claims (8)

1. A binder composition for a heat-resistant layer of a nonaqueous secondary battery, comprising a particulate polymer,
the particulate polymer comprises a cyano group-containing monomer unit and a hydroxyl group-containing monomer unit, and further,
a value M of the mole fraction of the hydroxyl group-containing monomer units in the particulate polymerOHA value S (μm) divided by the surface area of the particulate polymer2) To the obtained value (M)OH(S) is 0.40 or more.
2. The binder composition for a heat-resistant layer of a nonaqueous secondary battery according to claim 1, wherein the volume average particle diameter of the particulate polymer is 0.30 μm or less, and
the molar fraction of the hydroxyl group-containing monomer unit in the particulate polymer is 0.02 or more.
3. The binder composition for a non-aqueous secondary battery heat-resistant layer according to claim 1 or 2, wherein the molar fraction of the cyano group-containing monomer unit in the particulate polymer is 0.07 or less.
4. The binder composition for a heat-resistant layer of a nonaqueous secondary battery according to any one of claims 1 to 3, wherein the degree of swelling of the particulate polymer in an electrolyte solution is 8.0 times or less.
5. A slurry composition for a heat-resistant layer of a nonaqueous secondary battery, comprising a binder composition for a heat-resistant layer of a nonaqueous secondary battery according to any one of claims 1 to 4 and nonconductive particles.
6. The slurry composition for a heat-resistant layer of a nonaqueous secondary battery according to claim 5, wherein a volume average particle diameter of the non-conductive particles is 0.7 μm or less.
7. A heat-resistant layer for a nonaqueous secondary battery, which is formed using the slurry composition for a heat-resistant layer for a nonaqueous secondary battery according to claim 5 or 6.
8. A nonaqueous secondary battery comprising the heat-resistant layer for a nonaqueous secondary battery according to claim 7.
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